Preparation of jet fuels



United States Patent 3,231,628 PREPARATION OF JET FUELS Herman S. Bloch,Skokie, llL, assignor to Universal Oii Products Company, Des'Plaines,Ill., a corporation of Delaware No- Drawing. FiledJune 1, 1962, Ser. No.199,244 8 Claims. (Cl. 260-666) This application is acontinuation-in-part of my copending application Serial No. 783,146filed December 29, 1958, now abandoned.

This invention relates to a process for preparing jet fuels and moreparticularly to a process for preparing jet fuels which have moreadvantageous characteristics.

The need for jet fuels is increasing at a tremendous rate due to thegrowing use of this type of engine in the aviation industry plus anincrease in the interest in rockets. While the use of jet planes formilitary uses has been in efiect for a relatively long period of time,the civilian use of jet aircraft is now increasing at a rapid rate. Forexample, domestic airlines have just begun to use jet airliners forintracontinental and intercontinental passenger transports. Likewise,foreign airlines are also beginning to use more and more airlinerspowered by jet engines. As the use of jet aircraft increases, with therigid specifications of fuel consumption compared to the pay loadcarried as in the case of civilian airliners, and the requirements ofthe military aircraft for longer range, more sustained flights, the fuelrequired for the jet engines must of necessity become more efficient.let engines require up to five times as much fuel per hour as a pistonpowered plane and, therefore, the fuel which is required to operatethese engines must be highly eificient in operation. Many types of fuelare now being used to power jet engines, among which are kerosene andother hydrocarbontype fuels. The hydrocarbon fuels which are designedfor jet engines and/ or for rocket use have specifications which requirea high heat of combustion per pound of fuel as well as per gallon.Therefore, with both the volume and and the weight of the fuel adefinite factor in the specifications, a fuel which provides arelatively higher heat of combustion will be favored over that fuelwhich does not provide such a high heat of combustion per pound as wellas per gallon. In addition, the fuels which are required for the jetengines should have a relatively low mercaptan sulfur content and a lowsmoke volatility index. With regard to the latter point, the presence ofaromatics in the fuel has an effect on the smoke volatility of the fuelas well as affecting the elastomers which are used as sealants on fueltanks. These elastomers have a tendency to swell when the aromaticcontent of the fuel is too high and will later shrink and cause leakageto occur if a fuel which is low in aromatic content is used. Therefore,in view of all of the rigid specifications, the type of fuel which bestmeets all of the requirements has been found to consist of polycyclicnaphthenes. Such compounds have a higher heat of combustion per poundthan aromatic hydrocarbons, and a greater heat of combustion per gallonthan paraffin hydrocarbons. These polycyclic naphthenes may be preparedby the catalytic hydrogenation of polycyclic aromatic hydrocarbons suchas lube oil extracts, cycle stocks, etc., said hydrogenation beingcatalyzed by the presence of those catalysts containing nickel, cobalt,platinum, and other well known hydrogenation agents. Another source ofpotential jet fuels is found in feed stocks comprising hydrogenatedconjunct polymers which are derived from olefinic gasoline chargestocks.

In view of the aforesaid need for jet fuels, it is an object of thisinvention to provide a process for the preparation of jet fuels whichare more efli-cient in operation than some already in use.

A further object of this invention is to provide a process for thepreparation of jet fuels which possess a higher heat of combustion pergallon of fuel than those now in use Taken in its broadest aspect oneembodiment of this invention resides in a process for improving the heatof combustion of jet fuels comprising multi-ringed naphthenichydrocarbons containing alkyl substituted cyclo-, pentano groups whichcomprises isomerizing said alkyl substituted cyclopentano groups tocyclohexano groups in the presence of a Friedel-Crafts catalyst at atemperature in the range of from about 0 to about 150 C., and recoveringthe desired product.

A further embodiment of this invention resides in a process forimproving the heat of combustion of jet fuels comprising multi-ringednaphthenic hydrocarbons containing alkyl substituted cyclopentano groupswhich comprises isomerizing said alkyl substitutedcyclopentano groups tocyclohexano groups in the presence of an aluminum chloride catalyst at atemperature in the range of from about 25 to about C., and recoveringthe desired product.

Other objects and embodiments will be ,found in the following furtherdetailed description of this invention.

In preparing the desired jet fuels according to the process of thisinvention the thermodynamics of isomerization reactions must be takeninto consideration. The aforesaid thermodynamics of isomerization aresuch that the formation of cyclohexano groups is favored when utilizingrelatively low temperatures, that is, from about 0 to about C. while theformation of substituted cyclopentano groups is favored when usingrelatively high temperatures, that is, above about 150 C. Furthermore,when utilizing higher temperatures and more severe conditions, treatmentof alkyl substituted cyclopentano groups Will involvedisproportionationi.e., transfer of an alkyl substituent such as amethyl group from one naphthene ring to another. In addition the moresevere conditions which involve the use of higher temperatures will alsopromote ring scission with the formation of gaseous hydrocarbons andother undesirable hydrocarbons thereby radically altering the structureof the molecule which is involved in the reaction. For example, it isknown in the prior art that when a single ring polyalkyl substitutednaphthenic hydrocarbon is subjected to treatment at a temperature above150 C. in the presence of certain catalytic compositions of matter,disp'roportionation' arid ring scission will occur rather than theisomerization process of the present invention in which alkylsubstituted cyclopentano groups of a multi-ringed naphthenichydrocarbonare converted to cyclohexano groups.

As hereinbefore set forth the jet fuels which possess a higher heat ofcombustion per pound as Well as per gallon may be prepared by passingthe hydrogenated polycyclic naphthenic stocks containing alkylsubstituted cyclopentano groups over a Friedel-Crafts type isomerizationcatalyst at a relatively low temperature, that is, temperatures rangingfrom about 0 to about 150 C. and preferably in a range of from about 25to about 100 C. Under these conditions and under the influence of theparticular catalyst of the type hereinafter set forth the alkylsubstituted cyclopentano polycyclic cycloparaffin hydrocarbons areisomerized to a cycloheXane structure thus providing a product ofgreater density which has up to about 5% Patented Jan. 25, 1966 Increasein B.t.u./gal. Compound Density, D4 Relative to Compound (1),

' Percent (1) cnrfipI-ona 0.837 CH3 Examples of alkyl substitutedmulti-ring naphthenic hydrocarbons containing five-membered rings(CYCIOPGH': tano groups) will comprise hydrocarbons having the genericFormula I in which the various R substituents are independently selectedfrom hydrogen and alkyl radicals containing from 1 to about carbonatomsor more, at least one R on each ring being analkyl radical, andn isa number from' 0 to about 20. V Y Specific examples of these compoundsinclude 1,2-di (2-methylcyclopentyl)ethane, 1,2-di-(2-ethylcyclopentyl)ethane, 1,2-di-(2,3-dirnethylcyclopenty1)ethane,: 1,2-di-(2,3-diethylcyclopentyl)ethane, 1,2 di' (2,3,4-trimethylcyclopentyl)ethane, 1,2 di (Z-decylcylopentyl)ethane,

' absorbent support, such as, for example, alumina, or they may besuspended in a fluid medium, such as a hydrocarbon-Friedel-Crafts saltsludge. The supported catalysts are especially effective and long-livedwhen the support contains a small amount of a hydrogenation component,such as, for example, from about 0.05 to about 1% of platinum, and isused in the presence of hydrogen.

It is contemplated within the scope of this invention that the lowtemperature isomerization of multi-ring naphthenic hydrocarbonscontaining alkyl substituted cyclopentano groups to form cyclohexanogroups may be effected in any suitable manner and may comprise either abatch or a continuous type operation. One particular type of operationwhich may be used is the batch type in which a quantity of thehydrogenated compounds to be isomerized is placed in an appropriateapparatus along with the desired isomerization catalyst. The apparatusis then heated to a temperature in the desired range, that is,

from about 25 to about 100. C. and maintained thereat for apredetermined residence time, at the end of which time the apparatus andcontents thereof are cooled to room temperature. The reaction product isthen separated from the catalyst layer and subjected to conventionalmeans of recovery, that is, fractional distillation, etc. a

The process of'this invention may also be effected in a' continuous typemanner. Theuse of a Friedel-Crafts type catalyst of the typehereinbefore set'forth is especia ly adaptedto a fixed bed type ofoperation. In this operation the catalyst is disposed as a fixed bed ina reaction zone which is maintained at the proper operating conditionsof temperature and pressure. The reaction zone may comprise an unpack-edvessel or coil or may be lined with an aborbent packing material such asfire brick, dehydrated bauxite, alumina and the like. The charge stockto be isomerized 'is continuously charged thereto at aliquid hourlyspace velocity-in the range of from about 0.1 to about 10 or more, theliquid hourly space velocity being defined as the ,volume 1 of feedstock charged per volume of catalyst per hour, and passes over the fixedbed of catalyst in either an upward or down- Another'continuous type ofoperation which may be i used comprises the moving bed type in which thecatalyst 1,2-di-(2-dodecylcyclopentyl)ethane, 1,2'- di(octadecylcyclopentyl)ethane, etc., 2,6-dirnethyl[ 0,3,31bicyclooctane,2,6 diethyl[0,3,3]bicyclooctane, 2,6 dipropyl[0,3,3]bicyclooctane,1,2,6,7 tetramethyl[0,3,3]bicyclooctane, 1 ,2,6,7-tetraethyl [0,3 ,3bicyclooctane, 2,6Q-dioctyl [0,3 ,3] ,bicyclooctane, 2,6dinonyl[0,3,3]bicyclooctane, 2,6 didecy1[0,3,3 ]bicyclooctane, 12,6-dioctadecyl [0,3,3 bicyclooctane, 2,2'-dimethylbicyclopentyl, etc.It is to be understood that the aforementionedcompounds are onlyrepresentatives of the classes of compounds which may be isomerizedaccording to the process of this invention, and that said invention isnot necessarily limited thereto.

Examples of cyclohexano hydrocarbons which'will re- .sult from thisisomerization of the hereinbefore mentioned alkyl substituted,multi-ringed compounds containing cyclopento groups include Decalin,2,6-dimethyldecalin,

2,6-diethyldecalin, 1,6-dirnethyldecaJin;1,9-diethyldecalin,

1,2 di (cyclohexyl)ethane,'1,2-- di-(Z-ethylcyclohexyl)ethane,'bicyclohexyl, etc.

Friedel-Crafts type isomerization catalysts which may be used in theprocess of this invention include aluminum 7 chloride, aluminum bromide,zirconium chloride, ferric chloride, zinc chloride, etc. These'may beused in solid powdered form, or they may be'deposited on a solid and thereactants passconcurrently or countercurrently to each other through thereaction zone. In addition, another type of operation which may be usedis the slurry type of operation in which the catalyst is carried "intothe reaction zone as a slurry in the reactant. In both of the aforesaidtypes of reaction, as in the first continuous type of operation'whic'nwas described, the reaction products are continuously withdrawn from thereaction zone, separated from the unconverted effiuent and rejcovered byconventional means,'while the unconverted efiluent is recycled to forma' portion of the feed stock.

Theiollowing examples, which, however, are not intended to limit thegenerally broad scope of the present invention in strict accordancetherewith, are given to illustrate the process of thepresent invention.

"olefinic (polymer) gasoline. charge stock, having a boiling .point inthe rangeof from about 320 .to about 450 C., 'a density of D =0.874, amolecular weight of -375, a specific dispersion of'140 and a brominenumber of 167, which is indicative of four double bonds per molecule,was obtained from a fractional distillation. The .analysisof this cutwhich has an average formula of 27;5 47.s( n z i showed 87.34% carbonand 12.6% hydrogen,

This cut was hydrogenated at a temperature of 100 C. and an initialpressure of 1000 p.s.i.g. of hydrogen for four hours in a bomb over anickel catalyst. The resulting product was a water-white oil having adensity of D =0.854, a specific dispersion of 96.5 which is indicativeof a naphthene or parafiin, a molecular Weight of 390 and a brominenumber of 0. Analysis of this product disclosed 86.14% carbon and 13.82%hydrogen showing an average molecule having the empirical formula 27.552.5'

This product is then isomerized by treating the compound at atemperature of about 50 C. in the presence of 5% by Weight of aluminumchloride catalyst for a period of about 3 hours in a stirred autoclave,with a slow stream of hydrogen chloride bubbling through the liquid. Theresultant product then shows a density of D =.887, the specificdispersion, molecular weight and bromine number remaining substantiallyunchanged, while the boiling range is raised by an average of about C.,

Example 11 A conjunct polymer obtained by the reaction of aluminumchloride with a polymer gasoline charge stock is treated in a mannersimilar to that set forth in Example I above. The cut boiling from 320to 450 C. and having the same properties as those set forth above ishydrogenated over nickel catalyst at a temperature of 100 C. and aninitial pressure of 1000 p.s.i.g. of hydrogen for four hours. Theresultant water-White oil is then isomerized in the presence of twopercent by weight of aluminum bromide catalyst at a temperature ofapproximately 35 C. for a period of 3 hours, the resultant isomershaving a density of about D =.887, a higher boiling range than theunisomerized material, and a greater volumetric heat of combustion thanthat of the hydrogenated product before isomerization, Under these mildisomerization conditions, scarwly any cracking of the feed to gaseousand other light products occurs.

I claim as my invention:

1. A process for improving the heat of combustion of jet fuelscomprising multi-ringed naphthenic hydrocarbons containing alkylsubstituted cyclopentano groups which comprises isomerizing said alkylsubstituted cyclopentano groups to eyclohexano groups in the presence ofa Friedel- Crafts catalyst at a temperature in the range of from about 0to about 150 C., and recovering the desired product.

2. A process for improving the heat of combustion of jet fuelscomprising multi-ringed naphthenic hydrocarbons containing alkylsubstituted cyclopentano groups which comprises isomerizing said alkylsubstituted cyclopentano groups to cyclohexano groups in the presence ofan aluminum chloride catalyst at a temperature in the range of fromabout 0 to about 150 C., and recovering the desired product.

3. A process for improving the heat of combustion of jet fuelscomprising multi-ringed naphthenic hydrocarbons containing alkylsubstituted cyclopentano groups which comprises isomerizing said alkylsubstituted cyclopentano groups to cyclohexano groups in the presence ofan aluminum chloride catalyst at a temperature in the range of fromabout 25 to about C., and recovering the desired product.

4. The process of claim 3, further characterized in that said naphthenichydrocarbon is 2,6-dimethyl[0,3,3]bicyclooctane.

5. The process of claim 3, further characterized in that said naphthenichydrocarbon is 2,6-diethyl[0,3,3]bicyclooctane.

6. The process of claim 3, further characterized in that said naphthenichydrocarbon is 1,2,5,6-tetrarnethyl[0,3,3] bicyclooctane.

7. The process of claim 3, further characterized in that said naphtenichydrocarbon is 1,2,6,7-tetraethyl[0,3,3]bicyclooctane.

8. The process of claim 3, further characterized in that said naphthenichydrocarbon is a hydrogenated conjunct polymer derived from an olefiniccharge stock.

Thomas, Anhydrous Aluminum Chloride in Organic Chemistry, page 721relied on, Reinhold Publishing Corp., New York, 1941.

DELBERT E. GANTZ, Primary Examiner.

A'LPI-IONSO D. SULLIVAN, Examiner,

1. A PROCESS FOR IMPROVING THE HEAT OF COMBUSTION OF JET FUELSCOMPRISING MULTI-RINGED NAPHTHENIC HYDROCARBONS CONTAINING ALKYLSUBSTITUTED CYCLOPENTANO GROUPS WHICH COMPRISES ISOMERIZING SAID AKYLSUBSTITUTED CYCLOPENTANO GROUPS TO CYCLOHEXANO GROUPS IN THE PRESENCE OFA FRIEDELCRAFTS CATALYST AT A TEMPERATURE IN THE RANGE OF FROM ABOUT 0*TO ABOUT 150*C., AND RECOVERING THE DESIRED PRODUCT.